1. Field of the Invention
The present invention relates to a stripline for radio-frequency signals, having a signal conductor and at least one earth conductor, both being arranged on a substrate made from an electrically insulating material. The invention also relates to an attenuator as well as a terminating resistor.
2. Description of Related Art
What are used in high-precision attenuators and terminating resistors, for calibrating network vector analyzers for example, are striplines, and in particular what are referred to as “suspended striplines”. When the striplines are being sized, parameters which act in opposite directions have to be optimized in this case. On the one hand, the stripline and the substrate on which the stripline is formed have to be designed to be as geometrically small as possible, because at frequencies whose wavelengths are equal to or smaller than the geometrical dimensions of the structure, and in particular than the geometrical dimensions of the substrate, waveguide modes which produce undesirable electrical properties from the point of view of impedance matching are excited. On the other hand, the geometrical dimensions of the substrate set a corresponding limit to the maximum thermal load which the structure comprising the stripline and substrate is able to accept, which means that only a limited electrical power is able to be transmitted through the attenuator and the terminating resistor. At higher powers the entire structure would be thermally damaged or destroyed. Larger geometrical dimensions, of the substrate for example, would be desirable for higher powers, but these would at once result in a fall in the limiting frequency up to which the structure could be operated while still exhibiting the desired electrical properties.